Field of the Invention
This invention relates to compositions having at least one compound which inhibits the formation of Hemipteran stylet sheaths, degrades hemipteran style sheaths that have already been formed or deters or blocks hemipteran insects from feeding on plants, especially agriculturally important plants. The invention also relates to methods of using compositions of the present invention to inhibit the formation of hemipteran stylet sheaths, to degrade hemipteran style sheaths that have already been formed, or to deter or block hemipteran insects from feeding on plants, especially agriculturally important plants. This invention also relates to a method of preventing and/or reducing the transmission of vascular associated diseases (caused by hemipteran vector-borne pathogens) to economically important plants.
Description of the Related Art
Insect pests of plants can cause severe plant damage feeding activities initiated to draw nutritional needs from plant tissues. Of these, many plant feeding insects within the Hemiptera order feed by piercing the plant tissues and produce oral secretions that harden into a specialized feeding structure considered essential for insect survival. Many phytophagous hemipterans (true bugs) are characterized by common structural mouthparts (Forero, Revista Colombiana De Entomologia, Volume 34 (1), 1021, 2008) that penetrate host plants inter- or intra-cellularly to feed on contents of vascular tissues or other vegetative cell types. The Order Hemiptera is divided into four clade groups (suborders), the Auchenorrhyncha, Coleorrhyncha, Heteroptera, and Sternorrhyncha (for a systematic review of Hemiptera—see Forero, 2008, (Forero, 2008, supra)). The Sternorrhyncha (Dejean, Gibernau et al., Comptes Rendus De L Academie Des Sciences Seri Ili-Sciences De La Vie-Life Scineces, Volume 323 (5), 447-454, 2000; Howard, Insect On Palms, wallingford, UK; CABI Pub., 2001; Gullan, Encyclopedia of Insects, 2nd edn., V. H. Resh, Cardé, R. T., San Diego, Elsevier, 957-967, 2009) including (but not limited to) Psyllidae (e.g. psyllids), Aleyrodidae (e.g. whiteflies), Aphididae (e.g. aphids), Pseudococcidae (e.g. mealybugs), and Coccidae (e.g. scales); the Auchenorrhyncha including (but not limited to) Cicadoidea (e.g. cicadas), Membracoidea (e.g. leafhoppers and treehoppers), Fulgoroidea (e.g. planthoppers), and Cercopoidea (e.g. spittlebugs); and the Heteroptera including (but not limited to) Pentatomidea (e.g. squash bug), contain many agronomically important plant pests that are vectors of pathogens causing plant diseases resulting in vast crop losses worldwide (Backus, Serrano et al., Annual Review of Entomology, Volume 50, 125-151, 2005; Goggin, Current Opinion in Plant Biology, Volume 10(4), 399-408, 2007; Kempema, Cui et al., Plant Physiology, Volume 143(2), 849-865, 2007).
Phytophagous hemipterans feed by penetration of a stylet bundle into plant tissues. A common trait of these insects is the concurrent formation of a solidifying sheath structure, termed stylet sheath that encapsulates the stylet bundle while they penetrate into the plant tissues. As the stylets penetrate various plant tissues, they secrete liquid droplets that solidify to form a solid hollow tube extending from the leaf surface to the point of feeding within the plant tissue, often terminating in the plants vascular tissue (Miles, Advances in Insect Physiology, Volume 9, 183-255, 1972). A subset of these insects also feed more generally on the parenchyma and mesophyll cells of plant tissues, but still produce stylet sheaths as part of the feeding process. Watery and gelling sheath saliva represent two common forms of salivary secretions that are implicated in stylet sheath composition and hemipteran feeding (Miles 1972, supra; Miles, Biological Reviews of the Cambridge Philosophical Society, Volume 74(1), 41-85, 1999; Tjallingii, Journal of Experimental Botany, Volume 57(4), 739-745, 2006; Carolan, Fitzroy et al., Proteomics, Volume 9(9), 2457-2467, 2009; Moreno, Garzo et al., Entomologia Experimentalis Et Applicata, Volume 139(2), 145-153, 2011; Backus, Andrews et al., Journal of Insect Physiology, Volume 58(7), 949-959, 2012; Will, Steckbauer et al., Plos One, Volume 7(10), 2012). The exact function(s) of the stylet sheath in feeding are not known; however, trait conservation across phytophagous hemipterans (Backus, Serrano et al., Annual Review of Entomology, Volume 50, 125-151, 2005), implies biological importance. Stylet sheaths are thought to provide stability and directional orientation to the stylets during the piercing process (Walling, Plant Physiology, Volume 146(3), 859-866, 2008), to aid in proper feeding (Walling 2008, supra), to ‘cloak’ the stylets from host (plant) defense responses (Miles, 1999, supra), and to rapidly seal cell penetration points during stylet probing (Tjallingii and Esch, Physiological Entomology, Volume 18(3), 317-328, 1993; Will and van Bel, Journal of Experimental Botany, Volume 57(4), 729-737, 2006). This sealing effect is thought to block “plant sensing” of cell damage preventing the perception of increased oxygen and/or rapid changes in pressure, both of which could be signals for induction of plant defenses.
Commonly, stylet sheath initiation occurs concurrently with insect labium contact with host plant surfaces (Miles, Journal of Insect Physiology, Volume 3(3), 243, 1959). Observations indicate that once the insect's labial sensilla encounters a surface (plant or artificial membrane), this surface contact appears to initiate a salivation response from the insect (presumably initiated by sensory mechanisms within the labium) (Miles, Journal of Insect Physiology, Volume 2(4), 338-347, 1958). The secreted saliva that results is presumed to function in assisting the insect to determine the suitability of the surface for feeding. It has been suggested that solidification of sheath material requires interaction with host (plant) components (Lloyd et al., Ohio J. Sci., Volume 87, 50-54, 1987). Additionally, oxygen interactions have been suggested for proper gelling of the flange which is on the leaf surface and the sheath which is found within the leaf tissue (Tjallingii, J. Exp. Bot., Volume 57739-745, 2006; Miles, J. Insect Physiol., Volume 11, 1261-1298, 1965), with a recent report supporting this hypothesis (Will et al., PLoS ONE Volume 7(10), e46903, doi:10.1371/journal.pone.0046903, 2012). Numerous reports using artificial diet systems have allowed the visualization and study of stylet sheaths (Miles, 1999 supra; Miles, J. Insect Physiol., Volume 3, 243-255, 1959; Wang et al., Entomol. Exp. Appl., Volume 129, 295-307, 2008; Cherqui and Tjallingii, J. Insect Physiol., Volume 46, 1177-1186, 2000; Miles, J. Insect Physiol., Volume 4, 2090219, 1960; Miles, J. Insect Physiol, Volume 4, 271-282, 1960; Miles et al., Entomol. Exp. Appl., Volume 59, 123-134, 1991). Stylet sheaths associated with plant tissues begin with a flange (exterior) on the leaf surface, followed (interior) by a narrowing (‘neck’ region) as the stylet sheath traverses the upper/lower (outer) epidermis of the leaf (Brennan, Weinbaum et al., Biotechnic & Histochemistry, Volume 76(2), 59-66, 2001; Wang, Tang et al., Entomologia Experimentalis, Volume 129(3), 295-307, 2008). This is subsequently followed by a thicker sheath ‘shaft’ having a continuous sequential bulbous structure as it traverses the tissue to the target region where the sheath may remain as a single channel or branch laterally among the cells of the target tissues (phloem and/or xylem) (Brennan, Weinbaum et al. 2001, supra; Wang, Tang et al. 2008, supra; Lopes, Bonani et al., Entomologia Experimentalis Et Applicata, Volume 134(1), 35-49, 2010). Sheath material has been induced using a brushing technique in sharpshooter (Alhaddad, Coudron et al. Annals of the Entomological Society of America, Volume 103(3), 543-552, 2011); however, the shape of this induced solidified sheath material differs from those formed naturally (Leopold, Freeman et al. Arthropod Structure & Development, Volume 32(2-3), 189-199, 2003; Lopes, Miranda et al. Entomologia Experimentalis Et Applicata, Volume 134(1), 35-49, 2009).
P. W. Miles published a series of papers from the late 1950's to mid 1960's that generally indicate that stylet sheaths are proteinaceous (Miles, 1959, supra; Miles, Journal of Insect Physiology, Volume 4(4), 272-282, 1960; Miles, Journal of Insect Physiology, Volume 10(1), 147-160, 1964; Miles, Kinsey et al. Experientia, Volume 26(6), 611, 1964; Miles, Journal of Insect Physiology, Volume 11(9), 1261-1268, 1965; Miles, Journal of Insect Physiology, Volume 13(12), 1787, 1967); however, Miles' methods indicate that his conclusions may be limited to the flange portion of the insects' secretion (Oncopeltus fasciatus, milkweed bug) (Miles, 1959, supra) and not specific to the shaft or branching regions of the stylet sheaths. Subsequently, a host of papers have been published that associate proteins with hemipteran feeding and these indicate multiple proteins are secreted into plants during the probing/feeding processes of various hemipterans (Miles and Harrewijn, Entomologia Experimentalis Et Applicata, Volume 59(2), 123-134, 1991; Madhusudhan and Miles, Entomologia Experimentalis Et Applicata, Volume 86(1), 25-39, 1998; Cherqui and Tjallingii, Journal of Insect Physiology, Volume 46(8), 1177-1186, 2000; Tjallingii, 2006, supra; Will and van Bel, 2006, supra; Will, Tjallingii et al. Proceedings of the National Academy of Sciences of the United States of America, Volume 104(25), 10536-10541, 2007; Carolan, Fitzroy et al. 2009, supra; Cooper, Dillwith et al., Environmenatl Entomology, Volume 39(1), 223-231, 2010; Hattori, Tsuchihara et al., Insect Biochemistry and Molecular Biology, Volume 40(4), 331-338, 2010; Sahayaraj, Kanna et al., Journal of the Entomological Research Society, Volume 12, 37-50, 2010; Alhaddad, Coudron et al. 2011, supra; Backus, Andrews et al., Journal of Insect Physiology, Volume 58(7), 949-959, 2012; Will, Steckbauer et al. 2012, supra). These more recent publications refer to secreted materials that do not appear to have structural implications for stylet sheaths, but rather appear to have a molecular ‘effector’-like effects on the host plants (Miles and Sloviak, Experimentia, Volume 26(6), 611, 1970; de Ilarduya, Xie et al., Molecular Plant-Microbe Interactions, Volume 16(8), 699-708, 2003; Tjallingii 2006, supra; Will and van Bel 2006, supra; Will, Tjallingii et al. 2007, supra; Backus, Andrews et al. 2012, supra).
Recently, it was demonstrated that insects will produce stylet sheaths ‘in air’ (in dere) across a single layer membrane surface (without diet) in ‘mock feeding chambers’ (MFC) for Diaphorina citri (Psyllidae, Asian citrus psyllid), Aphis nerii (Aphididae, oleander aphid), Aphis gossypii (Aphididae, cotton/melon aphid), Toxoptera citricida (Aphididae, brown citrus aphid), Bemisia tabaci biotype B (Aleyrodidae, whitefly), Homalodisca vitripennis (Cicadellidae, glassy-winged sharpshooter), Ferrisia virgata (Pseudococcidae, striped mealybug), and Protopulvinaria pyriformis (Coccidae, pyriform scale) (Morgan, et al., PLoS ONE, Volume 8(4), 1-11, Apr. 2013). This membrane probing and stylet sheath formation by these insects is virtually instantaneously induced upon caging and membrane/labium contact with MFC membrane, and they subsequently deposit sheaths that are quite similar in comparison to those formed in plants. For D. citri ‘feeding’ across MFC membranes (membranes typically are either parafilm (common plastic ‘kitchen’ wrap) or Solvy™ stabilizer membrane (a water-soluble polyvinyl alcohol membrane)), solidification of the stylet sheath occurs rapidly after approximately 45 seconds post-secretion. The solidification process is rapid for stylet sheaths and does not require a lengthy time for solid structures to form. More recently, a technique to isolate intact stylet sheaths utilizing Solvy™ (Sulky of America, Kennisaw, Ga.) and differential filtration (Morgan, et al. 2013 supra).
While there are known methods for controlling hemipteran insects to reduce damage to plants, there is very little known on how to prevent hemipteran insects from feeding on a plant and/or spreading devastating diseases until the present invention. The present invention describes compositions of proteins (such as one or more enzymes and/or lectins) and/or small molecules (such as, but not limited to, metal chelating agents) and/or enzyme inhibitors which reduce or prevent Hemiptera feeding on plants. The present invention also describes methods for using these compositions for controlling Hemiptera damage to plants which is different from the related art methods.